1. Field of the Invention
This invention concerns a planar array antenna for receiving and transmitting linearly polarized waves having two parallel radiator planes, each with several radiator elements arranged in rows and columns, with the radiator elements of each radiator plane being coupled over a coupling network to a central point having the same amplitude and phase, and the two radiator planes receive or emit waves polarized perpendicular to one another.
2. Description of Related Art
The planar array antenna is designed as a radiator system for directional reception of extra-high frequency electromagnetic radiation fields on the basis of a planar invention concept by means of which directional information transmission systems can be operated, preferably in the areas of satellite-supported data transmission, audio transmission and video transmission. This invention primarily concerns the design of the individual radiators and their coupling to the network.
The scope of this invention also includes stationary and mobile telephone and information transmission based on satellite-supported communications transmission and the sector of terrestrial information transmission on the basis of defined point-to-point connections. Primary targeted application areas here include in particular the field of satellite-supported analog and digital signal transmission, preferably within the spectral range between 10.70 GHz and 12.75 GHz, as well as the field of terrestrial point-to-point transmission, preferably within the spectral range between 10.00 GHz and 10.40 GHz.
Planar radiator designs known at the present for reception of high-frequency electromagnetic radiation fields are based on electromagnetic excitation of slot fields with rectangular, square, circular or rhombic slot borders which are supplied electromagnetically by means of striplines with defined geometric dimensions.
The combination of an alternating arrangement of excited strip transmission lines or excited slots and the respective design of the slot contour determines the characteristics of the electromagnetic radiation field that can be generated. The known arrangements are based on generation of circularly polarized electromagnetic radiation fields by means of groups of slots energized in phase, with the individual slots being energized with a mutual offset of 90xc2x0 in space and time by means of pair of striplines with defined geometric dimensions, or they are based on generation of linearly polarized electromagnetic radiation fields by means of groups of slots energized in phase, with the individual slots being energized by means of a stripline with defined geometric dimensions, whose geometric arrangement determines the direction of vibration of the electric field vector. Known implementations of the design of the radiator elements have also been based on the use of conductor surfaces with defined geometric dimensions, consisting of one or more of the same or different surface elements galvanically linked or linked in a field-supported manner and having area edges in the form of a square, rectangle, circle or trapezoid, leading to energization of the slot fields, with the polarization being determined on the basis of the location of the signal input.
Implementations going beyond this have been based on the configuration of surface resonators in microstrip technology or coplanar technology having a square, rectangular or circular surface bordering. Both galvanic and field-supported embodiments of signal input are known here. Additional known implementations have been based on microstrip configurations in ring designs or frame designs with a resonant geometric ring length or frame length. The known implementations of the excitation networks for the case of the group arrangement are based on parallel power supply to the radiator elements or parallel power supply to series-supplied radiator subgroups. Microstrip technology, slotline technology, triplate technology or coplanar technology may be used for the implementation of these coupling networks.
Generation of two orthogonal polarizations is based on the known status of the manner of arranging the radiator elements along the surface normals of the slots or surface resonators. Known planar directional radiator arrangements with a high directional effect are configured exclusively as narrow band systems or, for the case of satellite-supported information transmission, they are configured as single-band systems. Signal input and output take place in a known manner by way of a hollow conductor with a capacitive probe, with the hollow conductor geometry imaging the propagation condition of the type of field of the highest cut-off wavelength.
The goal of this invention is the configuration of planar transmission and reception modules by means of which directional information transmission links, both direct and transponder-supported, can be designed within the framework of the mobile terrestrial telecommunications and information transmission sector using satellite-supported telecommunications lines.
The object of the present invention is therefore to provide a planar array antenna whose geometric dimensions are as small as possible, with the antenna having the broadest possible spectral band with a high surface efficiency and a high directional effect.
This object is achieved according to this invention by a planar array antenna having the features of claim 1. Additional advantageous embodiments are derived from the features of the subordinate claims.
The planar array antenna according this invention advantageously has square slots which have a much greater broad-band effect and a greater polarization purity in comparison with round slots. However, square slots have the disadvantage that they require more electromagnetic coupling plus the fact that adjacent radiator elements mutually influence one another. Furthermore, square slots take up more space, which has a negative effect on implementation of the power supply system. This is due to the fact that only the striplines of the coupling network energizing the slots can extend into the slot space, and the coupling network which connects the excited striplines to the coupling point cannot extend into the slot space. Therefore, a square slot with rounded corners is used as the optimum between electric broad band properties and the required geometric space requirements. Square or rectangular slots with other conceivable shaping of the corners or sides are also possible.
The individual radiator is energized by means of a piece of conductor projecting into the slot. The shape of the conductor, the shape of the borders of the slots and the position of the conductor relative to the slot determine the base point impedance of the xe2x80x9cslot-conductorxe2x80x9d radiator element. The radiator elements are connected at the proper impedance and in the same phase and amplitude by a power supply or coupling network which is also planar, and they are led to a common summation point (coupling point) . A parallel power supply between individual radiators is generally used here. However, this is not appropriate with individual radiators having a square slot shape due to the lack of space. Due to the need for coupling of individual radiators at the proper impedance and with low reflection and the need for impedance transformation, this yields corresponding conductor widths that largely rule out the practical implementation options. Therefore in the state of the art, at least two power supply lines must be provided between two slots, which leads to considerable electrical and mechanical problems and makes practical implementation virtually impossible.
This fundamental problem is solved with the present invention by using a new serial power supply technology between two adjacent radiator elements. Due to the serial power supply, it is possible to design the entire power supply system in a mechanically simplified manner while also solving the space problem in providing power to square slots. Furthermore, the electric properties of the power supply line are greatly improved, because there are no power supply lines running in parallel between the slots, and consequently there cannot be any electromagnetic coupling phenomena which would have a negative effect on the entire functioning of the system.
The power supply to the slots is provided through line segments arranged in alternation in the plane of the electric polarization (e-plane). Thus, all the radiator elements are always aligned and polarized in phase opposition by 180xc2x0. To guarantee in-phase power supply to all elements, a 180xc2x0 phase difference is produced by phase inversion between two adjacent slots. This form of power supply also has the advantage that energized parasitic waves that are capable of propagation and occur due to asymmetries in energization of the slot by the triplate power supply line are largely eliminated by the serial power supply, and their negative effects on the electric functioning are greatly reduced. The advantageous combination of square slot with rounded corners and serial power supply leads to very good electric characteristics with regard to the polarization purity, insulation, front- to-back ratio and area efficiency.
The energized striplines serve to energize a type of field or vibration within the slot which is determined by the geometry and contour of the slot as well as by the geometric position and geometry of the excited stripline. This means that the design of the resulting type of field or radiation from the slot is determined by the superimposing the source condition or energization condition determined by the arrangement and geometry of the stripline on the propagation or existence condition which is determined by the contour and geometry of the slot. The field type generation of the polarization state of the slot field is determined by the specific generation of a defined impedance profile within the slot space by means of the dimensions of the excited stripline in terms of both geometry and arrangement, so that both orthogonal linear polarization and orthogonal circular polarization are generated for the case of the same slot contour. As a complementary measure, for the case of identical energization elements, i.e. the same excited striplines, the design or existence conditions of orthogonal linear polarization as well as orthogonal circular polarization are produced by means of controlled generation of defined slot elements within the slot space by means of the contour or geometric design of the slot. Linear polarization can be converted to circular polarization by means of an additional polarizer.
To maintain the broad-band characteristic of the individual radiator and the power supply network, a broad-band frequency coupling between the common power distribution of the antenna and the downstream electronic system (LNC) is needed. The planar array antenna according to this invention has an adapted, low-reflection, broad-band frequency transmission from a coaxial line to a triplate line. The problem with this type of coupling is the implementation of an extra-high-frequency ground connection between the external coaxial conductor (ground) and the two ground lines of a triplate line with coupling at the rear. This problem has been solved by using a hollow profile segment. A good ground connection between the hollow profile segment, the slot masks and the coaxial input or output is crucial. The xe2x80x9chollow profilexe2x80x9d or xe2x80x9ctunnelxe2x80x9d thus formed is selected so as to permit output of the antenna signal power with the lowest possible reflection. The external form of the hollow profile segment is irrelevant for the electric properties and is determined on the basis of manufacturing factors. Thus, any desired number of mechanical hollow profile segment shapes are conceivable. The object of the present invention is explained in greater detail below together with additional embodiments thereof, as described in the following drawings also.